Laser tube

ABSTRACT

An especially inexpensive laser tube is formed having a mirror mount composed of a material which is not matched to the coefficient of thermal expansion of the mirror material and in that the material is either soft soldered or glued on with a glue that develops little gas.

This is a continuation of application Ser. No. 265,932, filed Nov. 2,1988 now U.S. Pat. No. 4,943,972.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related generally to a laser tube having atubular housing composed of a glass or ceramic material and including atleast one metal mirror mount with an integrated mirror.

2. Description of the Related Art

A laser tube is disclosed in U.S. Pat. No. 4,087,762 wherein mirrors areinserted into mirror mounts and are tightly hermetically joined theretovia glass solder. The mirror mounts have coefficients of thermalexpansion which are matched to that of the mirrors. This requires thatthe mirror mounts be formed of a relatively expensive material and thatthey have a particularly complicated structure, since a transition mustbe formed from the mirror mount to an end face terminating plate of thelaser tube and the terminating plate has a coefficient of thermalexpansion matched to that of the laser housing. In other words, theterminating plate of the laser is composed of a different materialhaving a different coefficient of thermal expansion than that of themirror mount.

SUMMARY OF THE INVENTION

An object of the present invention is to reduce the cost of a mirrormount on a laser tube without accepting a deterioration in the laserpower output from the laser. In a laser tube, such as for use in a gaslaser, having a housing tube composed of a glass or ceramic materialwith at least one metal mirror mount and an integrated mirror, the aboveobject is achieved by forming the metal mirror mount of a costbeneficial, or inexpensive, material that is not matched to thecoefficient of thermal expansion of the mirror and by providing themirror material with at least one solderable region and soldering themirror onto the mirror mount with a soft solder. Alternately, themetallic mirror mount of inexpensive material not matched to thecoefficient of thermal expansion of the mirror material is fastened tothe mirror by a glue that develops and emits only little gas.

The reference to an inexpensive or cost beneficial material herein areto a material which is inexpensive relative to considerably more costlymaterials that have a coefficient of thermal expansion matched to, forexample, the mirror material mounted thereon, and that are known for useas mirror mounts in laser tubes.

Both embodiments yield adequately vacuum tight and, thereby, elasticallydeformable connections between the mirrors and the mirror mounts thatresist the temperature stresses which can arise in the laser. Thehighest temperature stressing of the corresponding parts occurs when thelaser is being soldered together, as experience has shown. The two,recited embodiments provide low joining temperatures which are,therefore, advantageous by avoiding the ordinarily high solderingtemperature stresses which lie considerably above the stresses occurringin the operating mode of the laser. In the embodiment utilizing a glueto hold the mirror to the mirror mount, a high-grade, silver-filledepoxy resin is especially well suited for gluing the mirror.

A further improvement of the invention provides an especially compactstructure when the laser tube is terminated with an end disk of metalhaving a coefficient of thermal expansion adapted, or substantiallymatched, to that of the housing tube. A fully reflecting mirror of theresonator mirror pair is soldered or glued to the end disk in the insideof the laser tube.

An additional possibility for simplifying the manufacture of a lasertube is provided when at least one of the laser mirrors is cut from alarger mother mirror. By making a mother mirror and then dividing itinto a plurality of individual laser mirrors, considerable time andexpense is saved. The individual laser mirrors advantageously comprisequadrilateral surfaces and the quadrilateral surfaces are preferablyquadratic. However, the surfaces of the mirrors can also have otherquadrilateral shapes such as, for example, a rectangular shape, or atrapezoidal shape.

The laser mirrors of the present laser tube are advantageouslymanufactured in a method having the following method steps as shown inFIG. 4:

(a) a mother mirror having an area equal to the area of a plurality ofindividual mirrors is coated with a photoresist;

(b) the photoresist is hardened on the mother mirror;

(c) the mother mirror is sawn into individual mirrors, whereby the cutedges thereof are simultaneously provided with a chamfer;

(d) the individual laser mirrors are cleaned; and

(e) the photoresist is removed from the individual laser mirrors in aplasma incinerating system without leaving a residue thereon.

A plasma incinerating system consists of a chamber with a high-frequencycoil with which high-frequency ion plasma is generated in an oxygenatmosphere. The ion plasma burns off the photoresist without leaving aresidue on the mirrors.

An alternate method, shown in FIG. 5, is likewise advantageouslyutilized wherein the mother mirror is not sawn into individual mirrorsbut instead is scored and broken and, thereafter, the edges of theindividual mirrors are rounded using a hydrofluoric acid. The remainingmethod steps of this alternate method are the same as that cited above.

An advantageous method for adjusting the mirrors of a laser tube isprovided by the present invention wherein two integrated mirrors areprovided for the laser tube to form the laser resonator. After assemblyof the laser tube, a test beam having a wavelength which is onlypartially reflected by the mirrors is beamed into the laser tube and thetwo mirrors are adjusted after the reflections of the test beam at themirror surfaces. For example, the emission of a green helium-neon laseris advantageously utilized for the adjustment of a red helium-neonlaser. This method is particularly well suited for mirror adjustment inthose instances where one of the mirrors has been glued to a metalplate, since the test beam in these instances can be beamed into thelaser tube from only one side (the partially reflecting side) and sincea test beam which is fully reflected by the mirrors would hardlynoticeably pass through the first mirror so that the adjustment of thesecond mirror (glued to the metal plate) which is not visible from theoutside would no longer be practically possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross section of an embodiment of a laser tubeaccording to the principles of the present invention;

FIG. 2 is an enlarged fragmentary cross section of another embodimentshowing fastening of a laser mirror to the laser tube according to theinvention;

FIG. 3 is an enlarged fragmentary cross section of a further embodimentof the invention showing an alternate means of fastening the lasermirror to the laser tube;

FIG. 4 is a block flow diagram showing one embodiment of a method formanufacturing mirrors according to the present invention; and

FIG. 5 is a block flow diagram of a second embodiment for manufacturingmirrors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a housing tube 1 is formed of a glass or ceramic material andis terminated at one end with a metal cap 2. The metal cap 2 hassubstantially the same coefficient of thermal expansion as that of theglass or ceramic laser tube 1 to prevent thermal stress therebetween.

A tube 3 is composed of a relatively inexpensive material that isinserted into the metal cap 2 in the direction of the laser emission.The tube 3 may be of, for example, copper or steel as suitable,inexpensive materials. The tube 3 has a widened, flange-like end 7facing directed away from the metal cap 2 and serving as a mirror mountfor a mirror 6. The mirror 6 is joined to the tube 3 in vacuum-tightfashion using either a glue or a solder as indicated at 4. Preferably,when a glue is used, the glue is of a type which exhibits little gasemission and, in one embodiment, is of a high-grade silver-filled epoxyresin. Such glue also has a high thermal conductivity and provides goodheat transmission from the mirror 6 to the flange 7 of the tube 3.

A bead, or restricted portion, 5 of the tube 3 is provided between thecap 2 and the flange 7 so that the angle of inclination of the mirror 6can be adjusted relative to the laser tube 2 by deforming the tube 3 atthe bead 5.

A face plate 9 is mounted at an opposite end of the housing tube 1. Theface plate 9 serves as a mirror mount in that a mirror 8 is gluedthereonto with a glue 4 or by a soft solder. The face plate 9 iscomposed of a material having a coefficient of thermal expansionsubstantially matched to that of the housing tube 1. The glue 4 exhibitsadequate elasticity so that the mirror 8 does not detach or deform evengiven the anticipated temperature fluctuations in the laser parts. Thisis further promoted by supporting the mirror 8 on a metal plate, wherethe mirror 8 is, first, kept extremely thin so that it is not exposed tothe vacuum pressure, and second, preferably has an extremely small areawhich needs only correspond to the beam diameter. The glue 4 exhibitsgood thermal conductivity so that improved heat elimination from themirror 8 to the face plate 9 is provided. Furthermore, the thinner andsmaller the mirror 8, the less pronounced the warping of the mirror as aresult of temperature fluctuations.

The joint between the face plate 9 and the housing tube 1 can also beformed by a glue of the above-described type; however, it can also beexecuted with a soft solder technique. In both instances, thetemperature stress for the glue 4 at the mirror 8 is kept adequatelyslight.

The mirror 8 may be applied lying precisely parallel to the face plate 9so that it is generally adequate to align the face plate 9 exactlyperpendicular to a discharge channel 23 in a capillary tube of thelaser. To provide a means for additional, subsequent correction of themirror position, an adjustment pin 10 is attached to the face plate 9which permits slight bending of the face plate 9. As needed, theadjustement pin 10 is surrounded by an annular zone 11 having arelatively thin wall thickness for better bending of the face plate 9.

In FIG. 2 is shown schematically the fastening of a mirror 12 with aglue 4 to a metal plate 14, whereby the metal plate 14 is soldered to ametal tube 13 with a ring of solder 15. This embodiment enablesespecially small mirrors to be used in combination with a mirror mountof a standard type. It likewise has the advantage that the metal tube 13and the metal plate 14 can be manufactured of an inexpensive material.The glued location of the mirror 12 is especially small in area so thatany deformations, such as thermal deformations, in this area are keptspecially slight.

Referring to FIG. 3, an embodiment is shown wherein a mirror 16 iscoated with a solderable metal layer 17, the metal layer 17 leaving freea beam passage region 18. The metal layer 17 is soldered to a ring 20 ofmetal via solder 19. The ring 20 is firmly seated on a relatively thinmetal tube 21. A further ring 22 is secured to the metal tube 21 at aslight distance from the first metal ring 20. The rings 20 and 22 areadvantageously soldered onto the metal tube 21; in many instances,however, it is adequate to simply press the rings 20 and 22 onto themetal tube 21. The rings 20 and 22 and the metal tube 21 areadvantageously composed of copper. Copper is a material which can beeasily soldered and is ductable so that bending of the tube 21 in theregion between the two rings 20 and 22 is easily possible to provideadjusting of the mirror 16. The embodiment of FIG. 3 allows especiallysmall dimensions for the mirror mount. In an alternate embodiment of theinvention, the ring 20 may be joined to the tube 21 in one piece, suchas by flaring the end thereof. In this case, it is recommendable tomanufacture this combined part with an extrusion process.

Thus, an especially inexpensive laser tube is formed which includes amirror mount composed of a material not matched to the coefficient ofthermal expansion of the mirror material and in which the mirror iseither soft soldered on or glued on with a glue that develops littlegas. The invention is especially utilized for inexpensive gas lasertubes.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

We claim:
 1. A method for manufacturing mirrors, comprising the stepsof:coating a mother mirror having an area equal to that of a pluralityof individual mirrors with a photoresist; hardening said photoresist;sawing said mother mirror into said plurality of individual mirrors,including providing cut edges of said individual mirrors with a chamfer;cleaning said individual mirrors; and removing said photoresist free ofresidue in a plasma incinerating system.
 2. A method for manufacturinglaser mirrors, comprising the steps of:coating a mother mirror having anarea equal to that of a plurality of individual mirrors with aphotoresist; hardening said photoresist; sectioning said mother mirrorinto said plurality of individual mirrors by scoring and breaking;rounding edges of said individual mirrors with hydrofluoric acid;cleaning said individual mirrors; and removing said photoresist free ofresidue in a plasma incinerating system.